With automatic transmissions of motor vehicles, which use positive-locking shifting elements in addition to friction-locking shifting elements, during gearshifts, the shifting command for closing the at least one positive-locking shifting element is triggered by means of the application of force (through, for example, electromechanical actuators, the application of hydraulic or pneumatic force, etc). by the transmission software with a certain temporal suspension prior to achieving the point of synchronization of the at least one positive-locking shifting element
Through this, after the expiration of the existing delays (in particular, signal propagation delays, hydraulic delays, the covering of the stretch for the closing of the positive-locking shifting element, etc), a pre-defined differential rotational speed window for the actual single-track process for the positive-locking shifting element is met.
This approach is especially important if, upon a downshift and the engagement of a gear, one engaged shifting element is a positive-locking shifting element.
In particular with hydraulically actuated positive-locking shifting elements in automatic transmissions, the temporal suspension prior to reaching the point of synchronization is strongly dependent on the temperature of the transmission oil.
The required temporal suspension for the triggering of the closing of a positive-locking shifting element may be determined from trials, and in an automatic transmission is calculated from the turbine speed gradient.
If, after the triggering of the signal for the closing of the positive-locking shifting element, a spontaneous change to the turbine speed gradient exceeding a predetermined threshold value arises, the differential rotational speed window necessary for the harmless engagement of the positive-locking shifting element, in a disadvantageous manner, can no longer be achieved because of the very low shift time of the shifting element up to the form lock, even through counter-measures.